Reducing Rollback Overhead In Time-warp Based Distributed Simulation With Optimized Incremental State Saving

Abstract

Distributed simulation employing the Time Warp mechanism suffers from the enormous amount of memory it uses for state saving. The main goal of this paper is to address this problem by introducing an incremental state saving technique with an optimized rollback mechanism. This method is especially suitable for simulations with large simulation states and a small amount of state change from one simulation step to the next. A very common example of such a simulation environment is digital logic simulation with up to a few hundred thousand signal and element states with only a small number of signals changing between two simulation steps. The event queue-indispensable part of every discrete event simulation system-is used as a management tool for incremental state saving, thus reducing administration overhead drastically. An optimized rollback mechanism ensures that only those parts of the simulation state are restored which have to be updated to the rollback time. Results on the experimental observation of memory usage for incremental state saving and time performance show the effectiveness of the introduced mechanisms on our Time Warp system.